XML Demystified

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XML Demystifi ed
Number of
Occurrences
DTD minOccurs maxOccurs
Zero to many * Zero Unbounded
One to many + One Unbounded
Zero or one ? Zero One
Table 4-1 A Comparison Between minOccurs and maxOccurs
If you don’t specify the minOccurs and maxOccurs attributes, the default value
is one.
With DTDs you learned how to reference multiple DTDs to form the definition
of an XML document. An XML schema has a similar mechanism. You can use xs:
include, which is basically the same as copying and pasting the referenced schema
into the current schema. It doesn’t allow for any type of override of or alteration to
the schema. The syntax looks like this:
This tells the processor to include the customer.xsd definition. You can also use
xs:redefine to include an external schema. xs:redefine allows you to alter the
definitions in the remote file:
… new definitions …
Looking Ahead
An XML schema is another way to describe the structure of an XML document. The
XML schema defines the building blocks used to build the XML document, similar
in concept to the document type definition (DTD).
The XML schema language is used to create the XML schema. Each statement
in the XML schema languge begins with